This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 19981830 filed in Norway on Apr. 23, 1998; the entire content of which is hereby incorporated by reference.
The present invention relates to a method for improving transmission between terminals in a telecommunication system.
More specifically, the present invention relates to a method for improving transmission between fax machines.
The present invention may also be said to relate to an improved utilisation of the protocols used for such fax transmission.
The present invention has been developed in connection with overcoming the problem of long delays in modern telecommunication systems in a fax transmission.
Modern telecom systems may have long delays because a series of satellite jumps plus mobile infrastructure are applied. The protocols obeyed by fax machines were made in times where such long delays during the set-up and transmission periods would be a sign of unreliable connection. The protocol timer values are fixed, which severely reduces the possibility to tune the communication.
Known Solutions
There are essentially three basic strategies:
Request Repetitions
One general strategy is to forward commands from one fax to the other while returning a request back for the repetition of the command already received. This repetition request will make the first fax set its timer again, and the hazards that its critical timer will expire, are eliminated.
This kind of solution come in two variants, one using only T.30 commands and one applying lower level HDLC frames.
WO 92/02100 (Motorola)
To prevent two different facsimile timers from expiring during communication between two such machines connected to the GSM environment, a reset timer command (e.g. a command repeat signal) is automatically sent by the interface.
WO 95/22224
To prevent facsimiles to timeout due to long satellite delay, after a period t1, a holding signal is sent. After a further period t2 a command repeat signal is sent, so that the transmitted signal is repeated if the called terminal has not transmitted a response.
Response Anticipation
The second strategy is to anticipate the acknowledgement from the second fax and send confirmation to the first fax in order to keep it happy and within its time limits. In most of these situations the anticipation will be correct, but in those cases where problems are detected, recovery action must take place.
Fax Mail Box
The third strategy is to buffer the whole fax in a fax mail box and retransmit it at a later point in time.
Problems with Known Solutions
The known solutions are more time-consuming and probably less robust for variances in the fax vendor implementations.
Request Repetitions
The problem with this kind of solution is that it cannot be applied in all situations as T.30 has no general request for repetition.
Response Anticipation
The problem with this is mainly that it relies upon fax vendors to comply with the same interpretation of T.30 in situations which T.30 originally did not foresee. This holds for the recovery actions when the anticipation does not hold.
Fax Mail Box
The main problem with this solution is that it exaggerates the delay. This means that the use of buffer space is more than needed, and that relatively synchronous desires, such as the request for combined speech and fax, cannot be properly handled.
An object of the present invention is to provide a method which solves the problem of long delays in modern telecommunication systems in a fax transmission.
Another object of the present invention is to provide a method which is more robust towards variances in fax implementations.
Still another object of the present invention is to provide a method giving extra flexibility where the standard constant delays in fax transmission may become too short.
Still another object of the present invention is to provide a method in which the delay problems of any protocol used in such point-to-point transmission, may be overcome.
The above objects are achieved in a method as stated in the preamble, which according to the present invention is based on the assumption that the total-connection between two fax machines are divided in at least two separate connections.
More specifically this method could be implemented by introducing a device which may be termed an xe2x80x9cinterceptorxe2x80x9d, for example an interceptor made by Ericsson which includes the implementation of a fax adapter.
Each of the two separate connections is assumed not to be subject to any delay problems.
Further features and advantages of the present invention will appear from the following description taken in conjunction with the enclosed drawings, as well as from the appending patent claims.